LONDON â€"  Queen Elizabeth II went to the races Saturday, at the start of a four-day celebration of her 60 years on the throne.

Later in the weekend she'll make a trip down the River Thames, then take in a concert -- all accompanied by tens of thousands of her subjects, coming out to fete a monarch whose longevity has given her the status of the nation's favorite grandmother.

Diamond Jubilee festivities officially began Saturday with a 41-gun salute fired by the King's Troop, Royal Horse Artillery at Horse Guards Parade in central London.

The 86-year-old monarch and her husband, Prince Philip, arrived at Epsom racecourse south of the capital for the Derby, one of the year's biggest horse-racing meetings. The queen waved to the 130,000-strong crowd as she was driven down the racecourse in a Bentley bearing the Royal Standard before settling down to watch the races from the royal box.

The monarch is a racing fan and horse breeder who reads the Racing Post each day over breakfast, although unlike many of her subjects she does not gamble.

The queen took the throne in 1952 on the death of her father, King George VI, and most Britons have known no other monarch.

Despite cool, damp weather in much of the country, hundreds of thousands of people are expected to participate in celebrations, including street parties, Sunday's 1,000-boat flotilla down the River Thames and a Monday pop concert in front of Buckingham Palace featuring Elton John and Paul McCartney.

Jubilee events end Tuesday with a religious service at St. Paul's Cathedral, a carriage procession through the streets of London and the queen's appearance with her children, grandchildren and great-grandchildren on the palace balcony.

Prime Minister David Cameron -- the 12th British leader of the queen's reign -- paid tribute to the monarch's "extraordinary level of physical energy, mental energy, and above all devotion to her people, to the institutions of this country, to the way our democracy works."

Not everyone in Britain will be celebrating. The anti-monarchist group Republic plans a riverbank protest as the flotilla goes by on Sunday, followed by a pub night where royal refuseniks can drown their sorrows.

With pictures of the monarch splashed across newspaper front pages, the left-leaning Guardian provided a button on its website that removed all jubilee stories.

But many Britons embraced the jubilee spirit -- a tribute to a monarch whose popularity cuts across all ages, social classes and political affiliations.

Writers and religious leaders used the occasion to reflect on how Britain has changed over the queen's reign, from a war-scarred imperial power to a middle-sized power with oversized cultural clout.

Bishop of London Richard Chartres said the queen's steadfast presence had helped the country adjust to rapid change.

"The quiet dignity of the queen and the way in which she and her family have reached out to include newly established British communities has provided a focus for continuing but expanding national self-respect and so has assisted the peaceful transformation of our national identity," he wrote in a jubilee pamphlet.